<template>
  <scroll
    class="listview"
    :data="data"
    ref="listview"
    :listenScroll="listenScroll"
    @scroll="scroll"
    :probeType="probeType"
  >
    <ul>
      <li
        v-for="(group,index) in data"
        class="list-group"
        :key="index"
        ref="listGroup"
      >
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li
            v-for="(item,index) in group.items"
            class="list-group-item"
            :key="index"
            @click="selectItem(item)"
          >
            <img
              v-lazy="item.avatar"
              class="avatar"
              alt=""
            >
            <span class="name">{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <div
      class="list-shortcut"
      @touchstart.stop.prevent="onShortCutTouchStart"
      @touchmove.stop.prevent="onShortCutTouchMove"
      @touchend.stop
    >
      <ul>
        <li
          v-for="(item,index) in shortcutList"
          :data-index="index"
          class="item"
          :key="item"
          :class="{'current':currentIndex===index}"
        >
          {{item}}
        </li>
      </ul>
    </div>
    <div
      class="list-fixed"
      v-show="fixedTitle"
      ref="fixed"
    >
      <div class="fixed-title">{{fixedTitle}}</div>
    </div>
    <div
      v-show="!data.lenght"
      class="loading-container"
    ></div>
  </scroll>
</template>
<script>
import scroll from 'base/scroll/scroll'
import { getData } from 'common/js/dom'
const ANCHOR_HEIGHT = 18
const TITLE_HEIGHT = 30
export default {
  props: {
    data: {
      type: Array,
      default () {
        return []
      }
    }
  },
  // 下面的data会被vue实时监听  与dom做交互
  data () {
    return {
      scrollY: -1,
      currentIndex: 0, // 当前显示的
      diff: -1
    }
  },
  created () {
    this.touch = {}
    this.listenScroll = true
    this.listHeight = []
    this.probeType = 3
  },
  methods: {
    selectItem (item) {
      this.$emit('select', item)
    },
    // 私有方法放在下面，公共方法放上面
    onShortCutTouchStart (e) {
      let anchorIndex = getData(e.target, 'index')
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
      // console.log('ddd' + e.target.getAttribute('data-index'))
    },
    onShortCutTouchMove (e) {
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY

      let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
      console.log(this.touch.anchorIndex)
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta
      this._scrollTo(anchorIndex)
    },
    scroll (pos) {
      this.scrollY = pos.y
    },
    _scrollTo (index) {
      // 点击边界顶部和底部不做处理
      if (!index && index !== 0) {
        return
      }
      // 在上下边界滑动时   不做处理
      if (index < 0) {
        index = 0
      } else if (index > this.listHeight.length - 2) {
        index = this.listHeight.length - 2
      }
      this.scrollY = -this.listHeight[index]
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
      //  this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
    },
    _calculateHeight () {
      this.listHeight = []
      const list = this.$refs.listGroup
      let height = 0
      this.listHeight.push(height)
      for (let i = 0; i < list.length; i++) {
        let item = list[i]
        height += item.clientHeight
        this.listHeight.push(height)
      }
    }

  },
  watch: {
    data () {
      setTimeout(() => {
        this._calculateHeight()
      }, 20)
    },
    scrollY (newY) {
      const listHeight = this.listHeight
      // 当滚动到顶部  newY>0
      if (newY > 0) {
        this.currentIndex = 0
        return
      }
      // 在中间滚动
      for (let i = 0; i < listHeight.length - 1; i++) {
        let height1 = listHeight[i]
        let hieght2 = listHeight[i + 1]
        if (-newY >= height1 && -newY < hieght2) {
          this.currentIndex = i
          this.diff = hieght2 + newY
          return
        }
      }
      // 最后一个元素上限
      this.currentIndex = listHeight.length - 2
    },
    diff (newVal) {
      let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
      if (this.fixedTop === fixedTop) {
        return
      }
      this.fixedTop = fixedTop
      this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
    }
  },
  computed: {
    shortcutList () {
      return this.data.map((group) => {
        return group.title.substr(0, 1)
      })
    },
    fixedTitle () {
      if (this.scrollY > 0) {
        return ''
      }
      return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
    }

  },
  components: {
    scroll
  }
}
</script>
<style lang="stylus" scoped>
@import '~common/stylus/variable';
.listview {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background: $color-background;
  .list-group {
    padding-bottom: 30px;
    .list-group-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      font-size: $font-size-small;
      color: $color-text-l;
      background: $color-highlight-background;
    }
    .list-group-item {
      display: flex;
      align-items: center;
      padding: 20px 0 0 30px;
      .avatar {
        width: 50px;
        height: 50px;
        border-radius: 50%;
      }
      .name {
        margin-left: 20px;
        color: $color-text-l;
        font-size: $font-size-medium;
      }
    }
  }
  .list-shortcut {
    position: absolute;
    z-index: 30;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 20px;
    padding: 20px 0;
    border-radius: center;
    background: $color-background-d;
    font-family: Helvetica;
    .item {
      padding: 3px;
      line-height: 1;
      color: $color-text-l;
      font-size: $font-size-small;
      &.current {
        color: $color-theme;
      }
    }
  }
  .list-fixed {
    position: absolute;
    top: -1px;
    left: 0;
    width: 100%;
    .fixed-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      font-size: $font-size-small;
      color: $color-text-l;
      background: $color-highlight-background;
    }
    .loading-container {
      position: absolute;
      width: 100%;
      top: 50%;
      transform: translateY(-50%);
    }
  }
}
</style>